Stern construction for motor boats and the like



April 22, 1930. J. c. SMALL 1,755,709

STERN CONSTRUCTION FOR MOTOR BOATS AND THE LIKE Filed Bee 10, 1929 n.Duzezzior eioualiimztifimall 6' Byway 35 culties of getting availablebait,

Patented Apr. 22, 1930 iIISEJGQ JONATHAN coox SMALL, or raovrNcnrowN,MASSACHUSETTS STERN coNsrImoTIoNrort Moron Bears AND THE LIKE IApplicationfiled December 10,1929. Serial No. 413,020.

This invention relates to improvements in marine propulsionlandparticularly to the increasingof the speed of motor driven boats whichhave heretofore-been retarded by inv adequate relations between hulldesign at the stern and the propeller power. There have been manyandradical develop v 'ments in motor boat design particularly along thetype of the so-called speed boat, but in the morefsturdytypes of craftthe lighter I powered motors have'not been productive of increases inspeed suchas seemed reasonably tripe expected by the horse power madeavail- To illustrate the'princlples of invention, I call attentlon toa'type of craft in general use and well illustrating" the problem. Theseboats maybe readily distinguished from the'speedboat type in that theyare of generally deeper draft and generally of the squarer stern type.

.These are usually, but not necessarily of the duty type of motor boatin which certain oomlnessis required; and sea worthiness an absoluteprerequisite.

Such boats'represent the substantial interestsofdeepwaterbusiness suchas that of mostimportant. I q I I 7 of. illustration I cite the usualproper coast boatadapted for offshore work as for example the verypractical conditions under which the fisherman must operate. The modernmarket for the catch, the difiiof any and all season supply imposeconditions which call for sea worthy, capable craft, but of speedheretofore unknown." 'e The requirements for sucha boat are mostexacting and'theyare'difiicult to design. So

far, the practical ideal boat for such work has not been produced. Itherefore base my disclosure on my own experience in redee signing orreadapti-ng standard types' to a uniform improvement in performance; 7 l.Imay take as an -illustrative problem that of the squarestern, ratherdeep draft. keel I speed seemed to be of no avail. V

'1 type of the coastfisherman. Such boatshave 'u'sually been providedwith; powerful engines but even with ample engine power the fisherman.For such; sea worthiness is by original building,

the demands 7 less of reserve engine power.

soon reach a limit beyond which they cannot I I 'bedriven though-belowthat of theoretical engine capacity. i The problem Was to provide-forincreased speed without sacrificing the desired feature 5.5 of design. v1

The operation of such a square stern boat is greatlyaifected by thesuction at the stern, caused by the passage of the boat through thewater, resulting in a dragging'of a volume of 69 water of great weight.It .has been observed that this suction increases so as to reach itsmaximum when the boat is moving-at '12 knots an hour and when it is sogreat that with the ordinary equipment of a fishing vessel, 5 it ispractically impossible to exceed a speed I of 12 knots. The dragincreases very rapid- .ly as the speed is increased from ten miles toreason of the fact that the water not being solid tends to slip awayfrom the propeller I blades ;this slipping of the water is,.of course,

greatest toward the surface of the water .as the surface of thewaterindicates the way of least resistance. 1 l

My invention contemplates by addition or the presence of stern factorswhich prevent the stern settling under the submersion tendency of thepropeller and the back drag on the stern inselfalso the slippage of thepropeller thrust.

. In general, Iprovide on'each side of the stern'what, as shown, is abox like compartment structure in the nature .of a counter sponson andat a slight angle to the race of V the propeller.

The difliculties seemed to .ee that these 9 boats at certain speedspeculiar to their 'design developed a sterndrag that so rapidlydiminished the otherwise possible. acceleration as to make a practicalspeed limitregardand under such conditions, the propeller red sistancediminished so that added propeller Whilejmy invention is capable ofembodiment in original structures my immediate In addition practicalproblem was that of discovering the deficiencies of craft already builtand in "shown the same boat otherwise unchanged did twenty-two andone-half knots. .The practical difference in the service use er thisboat made one days work out of what had been one and one-half or twodays In such practice and by applying the principles of my invention onthe basis of removable auxiliary stern lifting members or sponson likecharacter, it is possible by test to make adjustment to make up for thestern sag differential between the stern design and the propeller power.

on so adjusted and fitted these members operate as follows In startingthe stern usually settles somewhat slightly submerging the auxiliarychambers. Thesettling is however, soon overcome and as the boat picks upspeed the stern rises to normal water line. This relieves the stern ofany back drag and the wake runs clean. Furthermore, the downward pitchof the box bottoms takes-slightly of the propeller race thrust Which notonly keeps the ster'n'sustained, but steadies the propeller race.

In practice my invention may find many embodiments.

general solution for an immediate demand.

The drawings therefore show an average type square stern motor boat ofwhatmight be called a general utility type. It is to be understood asofsuitable power engine equipment.

In the. drawings:

Fig. 1 is a side view of a stern equipped in accordance with myinvention. I

Fig- 2 a stern view thereof, and

Fig. 3 a bottom view. 7 V

Considering the problem of such a boat as is indicated there is thegeneral hull portionl framed on ;and having a stern 3 and counter 9.

general keel member 2 ,The details of design are not involved in "theapplication of principle.

As shown, the stern has an overhang and the propeller 4 is on a shaft 5which has a slight downward pitch.

To make simple thedisclosure I show but one and that acase of I suchordinary occurrence that it involves the With such a design I equip witha pair of lateral box cells sponson members. These consist oflongitudinal side members 6 and 7 fitted at their upperedges to conformto the contour of the counter and straddling the rudder post.

These sidem'embers 6 and 7 'are fitte'd with a bottom 8 the forward edge"of which is fitted to the hull at its line of contact.

The rear of each chamberis closed by an 'end piece 9.

Wherethe stern design is such as to permit this to overlapthe stern itmay be made to constitute a supporting member.

The ends 9 are scuppered as to accommodate any leakage.

The bottom members 8 are given a slight downward pitch so as to receivethe race of the propeller 4. This. steadies the thrust of at 10 in orderthe propeller and imparts to the stern a' slight upward resultant.

Furthermore, when such a boat as above suggested isfpropelled at a speedexceeding about twelve miles an hour each compartment'relieves itself ofall water that may be in it; thus creating a greater buoyancy under thestern of the boat.

When this condition or situation has been brought about the bottom ofthe compartment is still below the level of the water which isalongsidethe boat, being keptf-rom rushing in from the sides by the projectingsides of the compartment. It is also kept from coming in at the open endof the structure by the depression injthe wake caused by the drag ofthestern. The effect of this in greatly increasing the speed of the boatseems to result in further reducing the slippage, by reason ot thedecrease of friction due to the reduction of the displacement" and theresulting lightening of the load on the engine. 7

What I therefore claim and desire to secure by Letters Patent is:

1. In combination with the stern of a -mo- *tor driven boat, of a pairof stern sponson boxes disposed one on eachside of the rudder post andhaving a flat'bottom pitched slightly downwardlyand rearwardlyanddisposed above th'efpropeller race. 2. In combination with the stern ofa motor driven boat, of a pair of stern sponson boxes disposed one oneach side ottherudder post and havinga fiat bottom pitched 'sli-ghtlydownwardly and rearw'ardly and diSPOSQdQ- above the propeller race, andof displacementsubsta'ntially equal to the stern submersion tendency ofthe boat at maximum propeller speeds.

i 3. Incombination with the stern of a mo:

tor boat, pair of attached flat bottomed sponson's disposed one on eachside of the rudder post and having their bottom fat substantially normalwater line and slightly the propeller race.

downwardlyand re'arwardly inclined into the sides and bottom one on eachside of the rudder post, the box 4. In combination with the stern of amotor driven boat, a pair of stern chambers disposed one on each side ofthe rudder post and having a flat bottom pitched slightly downwardly andrearwardly and disposed above the propeller race and of displacementsubstantially equal to the stern submersion tendency of the boat atmaximum propeller speeds.

5. In combination with the stern of a motor boat, a pair of flat bottomcounter boxes disposed one on each and having their bottoms atsubstantially normal water line and scuppered at their rear ends. I

6. In combination with the stern of a-motor driven boat, a' pair ofboxes each consisting of sides bottom and end members, fitted to thecounter,

ends overlapping the stern and supported thereby. v

7. In combination'with the stern of a motor boat a pair of auxiliarychamber members disposed one under each counter an havlng a combineddlsplacement substantially counteractive of the submersion tendency ofthepropeller at maximum speed.

In testimony whereof I aflix my signature.

JONATHAN COOK SMALL.

side of the rudder post

